Optimization Of Extraction Process Of Macadamia Oil With New Aqueous Method And Application Of Its Defatted Meal

Macadamia kernel is rich in nutrients,a woody oil-bearing material which is potentially valuable and can be used as one of sources of high-quality oils and proteins.However,the commercial methods currently commonly used for extracting oils have various disadvantages.Therefore,it is necessary to develop an efficient and green oil extraction method.The studies described in this thesis optimized the parameters of a new aqueous method of extracting macadamia oil,and preliminarily analyzed the mechanism of aggregation of non-oil solids to release oils.Meanwhile,the physiochemical indexes,micro components,antioxidative activity and storing stability of oils extracted by different methods were analyzed and compared so that the quality of oils extracted by new aqueous method was evaluated.Finally,the nutritional composition and application of defatted meal were studied.The main research contents and conclusions are as follows:（1）On the basis of single factor experimentation,the response surface experimentation was carried out to optimize the parameters of new aqueous extraction method to of extracting macadamia oil.It was concluded that the optimal process conditions for the extraction of macadamia oil by the new aqueous extraction method are as follows:microwave baking power was 320 W,microwave baking time was 60 s,sieving mesh number was 250,the amount of water added was 1.2 m L/10 g Macadamia kernel slurry obtained after grinding（GMK）,agitation time was 40 min.Under the optimized conditions,the extraction rate of oil（OER）only after centrifugation was91.30%.When the residue from centrifugation was treated at 30°C for 12 h with ventilation,it was cold-pressed to obtain the defatted meal with an oil content of 5.99%corresponding to the total oil recovery rate（ORR）of 96.09%.Therefore,the new aqueous extraction method is a green and efficient oil extraction process.（2）The structure,particle size and moisture distribution of the defatted meal was analyzed by using low-field nuclear magnetic resonance,laser particle size analyzer and physical property analyzer.The results showed that free water combined with non-oil solids when GMK was treated with water,resulting in an increase in the bound-water content of the non-oil solids,corresponding to an increase in the particle size and hardness of the defatted meal mainly containing non-oil solids,which therefore caused the release of free oils.（3）The results of comparing and analyzing the physical and chemical indexes,fatty acid composition,bioactive substances and in vitro antioxidant capacity of new aqueous extraction macadamia oil（N-AEMO）,solvent-extracted macadamia oil（SEMO）,hot-pressed macadamia oil（HPMO）and cold-pressed macadamia oil（CPMO）showed that the new aqueous extraction oil（N-AEMO）has higher iodine value,the lowest conjugated diene（K232）value and the lowest conjugated triene（K270）value（which are75.91 g/100 g、0.90 and 0.034,respectively）.The acid value and peroxide value of N-AEMO（27 mg KOH/g,0.21 mmol/kg）are second only to those of CPMO（0.23 mg KOH/g,0.19 mmol/kg）,but the difference is not significant.The moisture and volatile content of the N-AEMO（0.084%）were between those of SEMO and HPMO,which met the national standard for safe edible oils.GC-MS analysis indicated that oils extracted by different methods contained 14 different fatty acids,of which the content of oleic acid and palmitoleic acid was the highest.The types and content of fatty acids in oils extracted by different methods were not significantly different.Therefore,extraction methods didn’t affect the types and content of fatty acids in oils.The N-AEMO had advantages in total phenols（53.16 mg/kg）,flavonoids（22.96 mg/kg）and squalene（346.19 mg/kg）content,and it had the second high content of sterols（2376.33 mg/kg）only after SEMO.The results of the study on in vitro antioxidant capacity showed that the IC50 value of DPPH radical scavenging rate（33.97 mg/ml）and ABTS radical scavenging rate（44.52 mg/ml）of N-AEMO were the lowest though its FRAP value was the highest（0.039μmmol Fe SO₄/g）.Therefore,N-AEMO had good physical and chemical quality,effectively retained bioactive compounds and had good antioxidant capacity.（4）The results of were used to studying the oxidative stability of oils obtained by different extraction methods by using infrared spectroscopy and Schaal oven method showed that the peroxide value of all oils increased with the extension of storage time,and N-AEMO had the smallest increase in peroxide value and the best storage stability during storage at room temperature.During the accelerated oxidation storage process,the infrared spectrum showed that the macadamia oils obtained from the four oil extraction methods had typically characteristic spectra in the region of 600-4000 cm^-1,and they had relatively identical absorption peak position and shape during 0 day of storage.In the late storage period,N-AEMO had the maximum value of absorption peak enhanced in the region of 3500 cm^-1-3400 cm^-1,and the spectral band was broadened.Under the accelerated oxidation condition,the measured results of Schaal oven method indicated that the peroxide value of HPMO was higher than that required by the national standard for safe edible oils when stored for 80 days,while that（10.2181mmol/kg、9.9057 mmol/kg and 9.5348 mmol/kg respectively）of N-AEMO,SEMO and CPMO after 90 days of storage,there is not significantly difference between N-AEMO and SEMO,but slightly higher than that of CPMO.Therefore,the above results show that N-AEMO has good storage stability..（5）The new aqueous extraction method can effectively retain the nutrients of defatted meal which had a high protein content（30.60%）.The protein had whole amino acids with a high lysine content,and essential amino acids accounting for 36.45%（identical to that（32.70%）of soybean protein）of the total amino acid content.The defatted meal was an excellent resource of food proteins.（6）For study on the application of defatted meal obtained by new aqueous method to Chinese noodles,single factor experimentation followed by orthogonal experimentation found the optimum formula as the following:20%defatted meal flour,80%wheat flour,4%gluten and 1%salt（adding 38%water to knead dough）.Although the excessive addition of defatted meal had a negative impact on the texture and cooking quality of noodles,the appropriate amount of addition increased the expansion rate of noodles after cooking to 142.55%,and reduced the cooking time to 3.73 min（good for the development of instant noodles）.In addition,the effect of ingredients including defatted meal,gluten,salt and water on the quality of noodles and the secondary structure of proteins was analyzed.The results of infrared spectrum analysis showed that the noodle samples with the addition of defatted meal had two obvious absorption peaks near 2854 cm^-1and 1744 cm^-1.The content ofβ-sheet andα-helix in the protein of the noodle sample decreased,and the content of random coil increased,which might mean that the structure of the noodle sample changed from order to out-of-order.These results were identical to that of studying on the microstructure of noodles by scanning electron microscope.Therefore,the above results indicate that it is feasible to apply defatted meal in flour products.（7）Under the condition of using the optimum technical conditions and the optimum formula,the noodles containing defatted macadamia meal obtained by direct-drying after traditional calendering and the wet noodles with defatted macadamia meal obtained after calendering by the traditional method were treated in a high-pressure steam sterilizer at 120°C for 5 min followed by drying were compared and analyzed with ordinary wheat noodles.The results indicated that compared with ordinary noodles,the addition of defatted meal significantly shortened the cooking time of noodles by 53.96%.At the same time,the addition of defatted meal significantly increased the adhesiveness,protein content,polyphenol and flavone content of noodles,with growth rates of 25.70%,54.33%,105.84%and 111.80%respectively.Compared with direct drying,high pressure steam treatment significantly reduced the content of polyphenols and flavonoids in the noodles with loss rates of 31.09%and 35.26%,respectively.but significantly improved the texture quality and taste of the noodles with elasticity and cohesion increased by 0.030 and 0.119,and adhesion decreased by 79.26%.In addition,the sensory scores of macadamia nut defat noodles obtained after direct drying and high-pressure steam treatment were 85.35 and 85.625,respectively,and there was no significant difference between the sensory scores of ordinary wheat noodles（85.22）.Therefore,the results showed that the addition of defatted meal enriched the nutritional value and taste of noodles,and improved the utilization rate of defatted meal,providing a theoretical basis for the development of flour products.